Hi Emma, if your parents aren't great flyers you could think about getting married in Italy - very romantic destination for it including Florence, Rome, Venice, and the Lakes - your parents could then catch a train there if they preferred!
Alternatively, depending on time of year you could look at the Greek Islands - they are really popular for weddings and you can have the ceremony in a traditional chapel or even on the beach. And of course Greece is a lot closer to fly to than the Caribbean or Indian Ocean.
Just some thoughts, hope they help. If you want any more advice - no obligation (!) - just contact me at www.topdrawerholidays.co.uk
Ian